Sensors having a deformable membrane

Abstract

A pressure sensing element has at least a housing containing a fluid. The housing has at least two moveable surfaces in contact with the fluid in the housing; There is a first moveable surface comprising a pressure application surface which, when moved towards, away from, into or out of the fluid, creates a change in fluid pressure and a second moveable surface in contact with the fluid in the housing comprising a membrane which, when deformed by pressure changes in the fluid, alters its electrical resistance. The membrane has two electrodes attached to deformable material in the membrane. The membrane may have an elastomer having conductive particles distributed therein. The elastomer may be a dielectric and the particles are conductive nanoparticles.

What is claimed is: 
     
         1 . A pressure sensing element comprising:
 a housing containing a fluid;   the housing having at least two moveable surfaces in contact with the fluid in the housing;   a first moveable surface comprising a pressure application surface which, when moved towards, away from, into or out of the fluid, creates a change in fluid pressure; and   a second moveable surface in contact with the fluid in the housing comprising a membrane which, when deformed by pressure changes in the fluid, alters its electrical resistance.   
     
     
         2 . The pressure sensing element of  claim 1  wherein the membrane has two electrodes attached to deformable material in the membrane. 
     
     
         3 . The pressure sensing element of  claim 2  wherein the membrane comprises an elastomer having conductive particles distributed therein. 
     
     
         4 . The pressure sensing element of  claim 3  wherein the elastomer is a dielectric and the particles are conductive nanoparticles. 
     
     
         5 . The pressure sensing element of  claim 3  wherein the conductive nanoparticles comprise carbon. 
     
     
         6 . The pressure sensing element of  claim 2  wherein the fluid in the housing comprises a gas. 
     
     
         7 . The pressure sensing element of  claim 2  wherein the fluid in the housing comprises a liquid. 
     
     
         8 . The pressure sensing element of  claim 2  wherein the housing comprises an elongate cylinder and the first moveable surface comprises a film at one end of the cylinder. 
     
     
         9 . The pressure sensing element of  claim 2  wherein the first moveable surface is separate from the second moveable surface a distance within the fluid of between 0.1 and 20 mm. 
     
     
         10 . The pressure sensing element of  claim 2  wherein the first moveable surface is separate from the second moveable surface a distance within the fluid of between 0.1 and 5 mm. 
     
     
         11 . The pressure sensing element of  claim 2  wherein the first moveable surface is separate from the second moveable surface a distance within the fluid of between 0.1 and 2 mm. 
     
     
         12 . The pressure sensing element of  claim 2  wherein the housing comprises a layer having a hole therein, with the first moveable surface at one end of the hole, the second moveable surface at a second end of the hole, and the fluid is present within the hole. 
     
     
         13 . The pressure sensitive element of  claim 2  wherein the membrane has a thickness of from 4 to 50 microns. 
     
     
         14 . The pressure sensitive element of  claim 2  having a source of current between 0.01 and 10 volts applied to one electrode and a current sensor on the second electrode. 
     
     
         15 . The pressure sensitive element of  claim 2  wherein the at least two electrodes of the sensor are in communication with both a power source and a processor. 
     
     
         16 . The pressure sensitive element of  claim 2  wherein the fluid between the first moveable surface is separated from the second moveable surface has a fluid volume that maintains a separation of at least a 0.01 mm/between the first moveable surface is separate from the second moveable surface when a force of 5 grams is applied to the first moveable surface. 
     
     
         17 . The pressure sensitive element of  claim 8  wherein the two electrodes of the sensor are in communication with both a power source and a processor. 
     
     
         18 . The pressure sensitive element of  claim 12  wherein the two electrodes of the sensor are in communication with both a power source and a processor. 
     
     
         19 . The pressure sensitive element of  claim 16  wherein the two electrodes of the sensor are in communication with both a power source and a processor. 
     
     
         20 . The pressure sensitive element of  claim 17  wherein the sensor comprises an elastic body of a silicone rubber containing a loading of between 0.5% and 3%, by total weight of conductive nanotubes. 
     
     
         21 . The pressure sensitive element of  claim 18  wherein at least two electrodes of the sensor are in communication with both a power source and a processor. 
     
     
         22 . The pressure sensitive element of  claim 5  wherein the sensor comprises an electrically conductive silicone rubber composite comprised of a liquid silicone rubber with a multi-wall carbon nanotube loading of between 1%-3% by weight and a hardness between 10 and 60 Asker C hardness. 
     
     
         23 . A method of detecting pressure comprising providing a current into a first of the electrodes of the two electrodes of the pressure sensitive element of  claim 2 , providing a voltmeter or ammeter to a second of the electrodes of the two electrodes, applying a force to the first moveable surface to cause changes in the current or voltage measured by the voltmeter or ammeter, and comparing changes in the current or voltage to a lookup table to identify an amount of pressure being applied against the first surface. 
     
     
         24 . A method of detecting pressure comprising providing a current into a first of the electrodes of the two electrodes of the pressure sensitive element of  claim 2 , providing a voltmeter or ammeter to a second of the electrodes of the two electrodes, applying a force to the first moveable surface to cause changes in the current or voltage measured by the voltmeter or ammeter, signals indicating the changes in the current or voltage are forwarded to a processor and the processor executes code to indicate, as a basis of the signals, amount of pressure being applied against the first surface.